1. Field of the Invention
The present invention relates to plasma processing methods. In particular, the present invention relates to a plasma processing method used for manufacturing semiconductor or liquid crystal display devices, for example.
2. Description of the Background Art
A plasma processing apparatus has been used for a process of manufacturing a liquid crystal display device or semiconductor device, for example. In the manufacturing process, plasma is used for film deposition, etching and ashing processes for example. Such a plasma processing apparatus is required to provide a stable plasma acting over the entire substrate plane to be processed, in order to process the plane in a uniform and stable manner, for example, in order to uniformly deposit a film on the plane.
Recently, in the fields of semiconductor device, liquid crystal and the like, a typical example thereof being a semiconductor memory device, substrates have considerably been increased in size. In particular, for a TFT (Thin Film Transistor) liquid crystal display device, a substrate may be employed that has its size ranging from 500 mm×500 mm to 1 m×1 m or greater. Here, it is required to use a plasma processing method according to which a stable plasma acts on the entire plane of such a large-size substrate to be processed, in order to enhance the uniformity within the processed plane of the substrate and increase the speed of processing the plane.
FIG. 6 is a schematic cross section showing a structure of a general plasma processing apparatus. Referring to FIG. 6, an operation of the plasma processing apparatus is briefly described.
A substrate 8 to be processed is transported into a vacuum process chamber 1. An ambient gas within vacuum process chamber 1 is thereafter discharged by exhaust means (exhaust tube 11, control valve 12 and turbo pump 13). The inside of vacuum process chamber 1 is accordingly maintained in a vacuum state. Then, a process gas is provided from a process gas source 6 through a process gas supply unit 7 into vacuum process chamber 1. Simultaneously, a substrate holder 9 and substrate 8 are moved to a desired position by lifting/lowering means 10.
On the other hand, a microwave generated by a plasma exciting power source 5 is propagated to a microwave entrance window 3 through a waveguide 4 connected to plasma exciting power source 5 and an opening on one end of waveguide 4. The microwave is further propagated from microwave entrance window 3 to a dielectric plate 2. The microwave is then radiated almost uniformly from dielectric plate 2 to a region facing the entire surface of substrate 8 in vacuum process chamber 1.
The microwave radiated into vacuum process chamber 1 excites the reactant gas to generate plasma. After the plasma is generated, a high-frequency power source 14 applies a bias from substrate holder 9 to substrate 8. The plasma thus produced can be used to process the surface of substrate 8. For example, by means of the plasma, a film can be deposited on the substrate surface or ashing can be performed thereon.
The end of the plasma process is determined by measuring any change in the radiation intensity of any substance in the plasma by using an optical sensor 15 attached to vacuum process chamber 1. Specifically, a signal indicating the radiation intensity change measured by optical sensor 15 is supplied through an arithmetic processing unit 16 to a microwave source control unit 17 for example, and accordingly the plasma is stopped from being generated.
In this way, simultaneously with supply of the process gas to the entire surface of substrate 8, the microwave is radiated uniformly thereto from dielectric plate 2 so that a substantially uniform plasma can be produced in the region facing the entire surface of substrate 8.
FIG. 7 is a flowchart illustrating a conventional plasma processing method. Referring to FIGS. 6 and 7, substrate 8 is transported into vacuum process chamber 1 (step S101, hereinafter indicated without “step”). Then, an ambient gas within vacuum process chamber 1 is discharged to generate a vacuum (S102). A process gas is thereafter supplied into vacuum process chamber 1 and the pressure in vacuum process chamber 1 is adjusted to a predetermined pressure (S103). Then, a microwave energy, for example, is radiated into vacuum process chamber 1 to excite the process gas and generate plasma. The generated plasma is used for performing a desired process such as etching for a predetermined time (S104 and S105). After this, supply of the microwave energy is stopped, and subsequently the reactant gas is discharged to produce a vacuum within vacuum process chamber 1 (S106). Then, the processed substrate 8 is transported out of vacuum process chamber 1 (S107) and accordingly the successive steps of the process are completed.
Suppose that substrate 8 to be processed is formed of stacked films including a Ti (titanium)-based thin film and an Al (aluminum) film and this substrate 8 is dry-etched by a process gas which is a mixture gas of Cl2 (chlorine) and Ar (argon). In this case, a problem as described below could arise.
It is known that the rate of etching the stacked films increases if the ratio of the Cl2 gas is raised. When a process gas containing Cl2 of a greater ratio is supplied to etch the Al film of the stacked films, a stable plasma can be produced. However, the plasma could become unstable when the Ti-based thin film is etched. For example, the plasma could flicker. Then, the stacked films may be processed by lowering the ratio of Cl2 with the purpose of causing a stable discharge. However, this means that the ratio of Cl2 which directly contributes to etching decreases so that the etching rate deteriorates.
In order to solve the problem above, a method is devised according to which an etching process is divided into two stages and the stacked films are respectively processed under different plasma generating conditions. Specifically, the Ti-based thin film is etched with a low Cl2 flow rate while the Al film is etched with a high Cl2 flow rate in order to render discharge stable and enhance the processing speed (etching rate). Such an etching method using the process divided into two stages is disclosed in Japanese Patent Laying-Open No. 11-111702 for example which shows, as a conventional technique, a process as shown in FIG. 8 employed with the purposes of controlling a tapered shape of a sidewall of an etched film and enhancing the processing speed.
Referring to FIGS. 6 and 8, as the process shown in FIG. 7, substrate 8 is transported into the chamber (S101), and the air within the chamber is discharged for generating a vacuum (S102). Then, stacked films of substrate 8 are etched. The process of etching the stacked films is divided into two stages, i.e., a first etching and a second etching. In the first etching stage, a gas for the first etching is supplied and the pressure is adjusted (S203) and thereafter the first etching is carried out (S204 and S205). After the first etching, application of microwave power is temporarily stopped and the second etching is thereafter carried out. As the first etching, a gas for the second etching is supplied and the pressure is adjusted (S206). The second etching is thereafter carried out (S207, S208).
After the etching, the air is discharged (S109) as done for the process in FIG. 7 and substrate 8 is transported out of the chamber.
The etching method shown in FIG. 8 has a problem concerning the processing speed as described below.
According to the process in FIG. 8, the microwave power is once stopped from being applied, between the first etching stage and the second etching stage. Therefore, there is an additional time to wait for vanishing of the plasma as well as regeneration of plasma. Then, the extra time is added to the time for the plasma process. Consequently, the total time from supply of substrate 8 to removal thereof after the plasma process increases, which leaves a problem in terms of enhancement of the processing speed.